The present invention relates to a disc clamping device for engaging an information recording disc such as an optical disc or an optical magnetic disc coaxially with a turntable.
As a conventional disc clamping device, a magnetic fixing device is shown in FIG. 3 in which 1 is a turntable, 2 is a spindle, 3 is a magnet embedded in the turntable 1, 4 is an information recording disc 4, 5 is a ferromagnetic centering hub on the disc 4, and 6 is a center hole in the centering hub 5.
The turntable 1 integrally fixed to the spindle 2 is designed to rotate the information recording disc 4. The centering hub 5 is fixed on the disc 4 by bonding. The center hole 6 of the centering hub 5 has such a diameter as fits on the spindle 2 with a specified clearance.
The sequence of fixing the information recording disc 4 on the above conventional disc clamping device is as follows. The spindle 2 is inserted into the center hole 6 of the centering hub 5 for centering the disc 4. Then, the magnet 3 attracts the ferromagnetic centering hub 5 thereby fixing the disc 4 on the turntable 1.
The above conventional device has the following problems. The spindle 2 is required to have such an accurate diameter as fits in the center hole 6 of the centering hub 5 with the specified clearance. However, the centering hub hole can differ in diameter from disc to disc. Some discs may have too small a centering hub hole for the spindle to fit in, and some may have too large a centering hub hole to properly center the discs, resulting in the center being displaced so that the recording/reading head cannot trace the tracks.
The disc clamping device has another problem for an information recording disc that has no center hole because of a manufacturing process-related reason. Supposing the spindle is inserted in the centering hub hole of such a disc, if the axial length of the spindle effective for engagement with the centering hub is greater than the thickness of the centering hub, the spindle end engages the disc face, preventing the disc from being fixed in the device.